The invention may be used for hardening liquid radioactive wastes by transferring them into a solid stable vitriform state suitable for long-term storage in special storages.
An apparatus is known for supplying different fractions of material (see, for example, U.S. Pat. No. 3,964,892, 1976), comprising a metal housing having a flat bottom, a refractory reflector positioned on the inner surfaces of the metal housing and the flat bottom, a tubular channel for discharge of the melt which is positioned in the flat bottom and has a reduced inlet aperture which is closed by means of a rod which controls the output of glass melt, electrodes positioned at an angle of 120 degrees, a coil-in-box cooler positioned on the external side of the upper part of the metal housing, a charging device and a turning-positioning mechanism for the rod.
The danger of operation with the apparatus is high because of the high chemical corrosion of the electrodes and the refractory reflector. The durability of the apparatus is low because of the burn-out of the electrodes and the short service life of the refractory reflector. Furthermore, during the discharge there is the danger of the occurrence of an emergency situation due to the danger of the tubular channel overheating, of its higher chemical corrosion due to the unguaranteed closure of its reduced inlet aperture because of the higher chemical corrosion of the rod and the tubular discharge channel, and also because of the danger of the formation of a hard-to-remove glass plug in the tubular discharge channel.
A Joule melter is known for processing radioactive wastes (see, for example, Europatent 0 137 579, 1985), comprising a steel casting closed at the top by a steel lid, the inner surface of which is lined with a refractory material. A jumper is positioned on the bottom part of the refractory material, an electrode of cylindrical shape is positioned around the jumper, wherein a partition of cylindrical shape having an aperture is positioned inside the electrode, while a starting heater is positioned on the external side. An outlet pipe for the discharge of glass melt is located in the center of the bottom part, this pipe being simultaneously a second electrode and with its upper part being covered by a truncated cone with an aperture. A pipe of large diameter for the discharge of waste gases, an inlet pipe for loading the radioactive wastes and vitrification agents, and also a movable plunger with a conical end-piece ensuring closure of the aperture of the truncated cone are positioned in the steel lid.
Due to the burn-out of the electrode of cylindrical shape, which is a part of the melter housing, and of the second electrode, which is an outlet pipe for the discharge of the glass melt, and also due to the higher carrying away of radio nuclides, there is high danger in the operation of the melter.
Since the jumper has a reduced, temporary service life, the durability of melter operation is also low. And due to the greater amount of time necessary to create a starting melt by means of the starting heater, the productivity is low.
This melter has a narrow field of use due to the fact that it is not possible to process dehydrated radioactive wastes which contain ion-exchange resins which during melting may plug the uncooled inlet pipe for loading, or to process moist radioactive wastes which contain ion-exchange resins which may cause short circuiting of the electrodes through the moist radioactive wastes which are on the surface of the glass melt.
The danger of the occurrence of an emergency situation during discharge is also present in the aforesaid melter due to the blocking up of the outlet pipe for the discharge of melt, the impossibility of clearing it with a plunger, the danger of its overheating, high chemical corrosion, and also its burning out.
A method and apparatus for vitrification of radioactive materials is known (see, for example, British patent 1, 239 710, 1971). The apparatus for vitrification of radioactive materials is a crucible provided with a cooling system and with an induction coil connected to a high frequency generator. On top the crucible is closed with a metal lid with apertures to which a calciner and a bunker with vitrification agents, which is provided with a vibrating feeder, are connected. There is a discharge device at the bottom of the crucible which is a discharge pipe provided with a water-cooled jacket and an inductance coil connected to a high frequency generator.
There is a high degree of danger during operation of the apparatus due to high chemical corrosion of the housing of the crucible, the danger of its mechanical breakdown in the presence of high thermal stresses caused by a large difference between the temperature on the outer and inner surfaces, and also due to an increase in the degree of votalization of radio nuclides due to the use of a calciner for calcinating radioactive materials.
Furthermore, the melter has reduced productivity due to the absence of a mixer for preliminary mixing of the calcinate of radioactive materials and the vitrification agents, and also due to the immobility of the inductance coil of the crucible.
The field of use of the apparatus is also limited due to the fact that it is not possible to process ion-exchange resins which due to their melting in the calciner will plug the inlet pipe for loading the calcinate of radioactive materials.
During the discharge an emergency situation may arise since there is no discharge gate and this may be the reason for unauthorized discharge of the glass melt from the crucible.